Heretofore, higher quality radiation detectors, including those based on ion chambers and proportional counters, have been hermetically sealed in order to provide long term stability with respect to the calibration accuracy and precision of the detector. This type of seal has led to the use of metals, glasses and ceramics and the associated sophisticated sealing processes in order to achieve the desired performance. The use of these materials, while providing the requisite seal introduces other problems including: limitations on the range of radiation energies that could be detected and/or measured; long term stability problems due to surface corrosion or passivation; poor resistance to shock and rough handling, e.g. metal to glass seals used for dosimeter charging switches short out the dosimeter when the instrument is dropped; materials used are not similar to tissue equivalent or air equivalent; and the materials used are not conducive to mass production requirements for civil defense.
Because dosimeters for civil defense must be made on a surge demand, dosimeters for civil defense have been made of injection molded plastic in order to take advantage of lower material and labor costs. These dosimeters were generally adequate for this purpose because the accuracy requirements are not strict. An accuracy of .+-.30% is adequate for making proper operational decisions which is well within the tolerances of plastic dosimeters. The accuracy of plastic dosimeters only varies as much as .+-.15%. However, these devices must be impervious to water vapor and mechanical shock in order to be used effectively in the expected high humidity and harsh conditions of the fallout shelter environment.
An example of a dosimeter which was designed for civil defense purposes and which is relevant to the present invention is disclosed in U.S. Pat. No. 4,306,154, issued on Dec. 15, 1981 to Williams et al and entitled, "Dosimeter." This U.S. Patent is incorporated herein by reference. It has been found, however, that the device described in this patent will not provide adequate operation in moist climates as well as after the device has experienced mechanical shock.